650
different phases formed during preparation of series of MgO-ZrO 2 mixed oxides by
coprecipitation method and their catalytic activity in aldol condensation of FUR with
acetone [132]. Two different phases (a cubic Mg x Zr 1−x O 2−x and c-MgO) were identified, and formation of these phases depends on the nominal Mg/(Mg + Zr) atomic
ratio. The cubic Mg x Zr 1−x O 2−x solid solution was obtained below the nominal atomic
ratio of 0.5, and a mixture of c-Mg x Zr 1−x O 2−x and c-MgO was formed above nominal
atomic ratio of 0.5. The Zr-O-Zr sites are inactive for the condensation reaction.
Two different active sites, Mg-O-Mg and Mg-O–Zr, exist on the surface of
c-MgO. With the increase in Mg amount in the solid, Mg-O-Zr sites are replaced
with the Mg-O-Mg sites and make the later active sites predominant at the higher
Mg concentration. The maximum concentration of Mg-O-Zr species was formed in
the 0.5MgZr catalyst. The relative intrinsic catalytic activity (per mol of Mg) of
identified active sites follows the following trend: Mg-O-Zr sites on MgO > Mg-O-Mg
sites on MgO ≈ Mg-O-Zr sites on Mg x Zr 1−x O 2−x . The overall activity of the catalysts
is the combined activity of these sites that are existed in different proportions in the
catalysts depending on the nominal atomic ratio. Desai and Yadav prepared LaMg
mixed oxide catalysts of varying mole ratio and studied for solvent-free crossed
aldol condensation reaction [125]. LaMg mixed oxide catalysts were prepared by
combustion and hydrothermal process, and the latter synthesis process provides
higher surface area and higher amount of medium to strong basic sites. La 1 Mg 3 catalyst prepared by hydrothermal process exhibits superior catalytic performance in
aldol condensation due to the presence of moderate to strong basic sites. About 96%
conversion of FUR with 98% selectivity of C 8 (FAc) fraction was obtained at
150 °C in 7 h.
Natural dolomite has also been used as solid base catalyst for aldol condensation
reaction. Dolomite is an abundant sedimentary carbonate rock consisting of alternate planner structures of Ca
2+
and Mg
2+
ions generating a nonideal basic chemical
compound of formula CaMg(CO 3 ) 2 . O’Neill et al. studied aldol condensation of
FUR using activated dolomite as solid base catalyst [133]. Activation of dolomite
by calcination and hydration generates catalytically active Ca and Mg hydroxides
with enhanced surface area and surface basicity. The activated dolomite is more
selective to C 13 (F 2 Ac) product due to the higher heat of adsorption of C 8 (FAc)
product.
Various nanosized magnesium hydroxide fluorides, MgF 2−x (OH) x , as different
base catalysts were demonstrated for aldol condensation reaction of FUR and acetone to produce C 13 (F 2 Ac) fuel precursor with high yield [134]. The tunable acidbase properties and high surface area make these catalysts appropriate for such type
of reaction. Also, this class of catalytic material does not require activation before
reaction, which is often performed in case of metal oxide base catalyst due to the
presence of carbonate species on the catalyst surface. The presence of fluoride stabilizes the basic sites even at low temperature. The optimum amount of MgF 2
(Lewis acid sites) and Mg(OH) 2 (medium-strength basic sites) determines the performance of the nanocomposite catalysts, and MgF 1.5 (OH) 0.5 exhibits the best performance for producing C 13 (F 2 Ac) fuel precursors. The effect of different crystal
structures of cerous phosphate as solid acid catalysts on their catalytic performance
M. Baithy et al.
different phases formed during preparation of series of MgO-ZrO 2 mixed oxides by
coprecipitation method and their catalytic activity in aldol condensation of FUR with
acetone [132]. Two different phases (a cubic Mg x Zr 1−x O 2−x and c-MgO) were identified, and formation of these phases depends on the nominal Mg/(Mg + Zr) atomic
ratio. The cubic Mg x Zr 1−x O 2−x solid solution was obtained below the nominal atomic
ratio of 0.5, and a mixture of c-Mg x Zr 1−x O 2−x and c-MgO was formed above nominal
atomic ratio of 0.5. The Zr-O-Zr sites are inactive for the condensation reaction.
Two different active sites, Mg-O-Mg and Mg-O–Zr, exist on the surface of
c-MgO. With the increase in Mg amount in the solid, Mg-O-Zr sites are replaced
with the Mg-O-Mg sites and make the later active sites predominant at the higher
Mg concentration. The maximum concentration of Mg-O-Zr species was formed in
the 0.5MgZr catalyst. The relative intrinsic catalytic activity (per mol of Mg) of
identified active sites follows the following trend: Mg-O-Zr sites on MgO > Mg-O-Mg
sites on MgO ≈ Mg-O-Zr sites on Mg x Zr 1−x O 2−x . The overall activity of the catalysts
is the combined activity of these sites that are existed in different proportions in the
catalysts depending on the nominal atomic ratio. Desai and Yadav prepared LaMg
mixed oxide catalysts of varying mole ratio and studied for solvent-free crossed
aldol condensation reaction [125]. LaMg mixed oxide catalysts were prepared by
combustion and hydrothermal process, and the latter synthesis process provides
higher surface area and higher amount of medium to strong basic sites. La 1 Mg 3 catalyst prepared by hydrothermal process exhibits superior catalytic performance in
aldol condensation due to the presence of moderate to strong basic sites. About 96%
conversion of FUR with 98% selectivity of C 8 (FAc) fraction was obtained at
150 °C in 7 h.
Natural dolomite has also been used as solid base catalyst for aldol condensation
reaction. Dolomite is an abundant sedimentary carbonate rock consisting of alternate planner structures of Ca
2+
and Mg
2+
ions generating a nonideal basic chemical
compound of formula CaMg(CO 3 ) 2 . O’Neill et al. studied aldol condensation of
FUR using activated dolomite as solid base catalyst [133]. Activation of dolomite
by calcination and hydration generates catalytically active Ca and Mg hydroxides
with enhanced surface area and surface basicity. The activated dolomite is more
selective to C 13 (F 2 Ac) product due to the higher heat of adsorption of C 8 (FAc)
product.
Various nanosized magnesium hydroxide fluorides, MgF 2−x (OH) x , as different
base catalysts were demonstrated for aldol condensation reaction of FUR and acetone to produce C 13 (F 2 Ac) fuel precursor with high yield [134]. The tunable acidbase properties and high surface area make these catalysts appropriate for such type
of reaction. Also, this class of catalytic material does not require activation before
reaction, which is often performed in case of metal oxide base catalyst due to the
presence of carbonate species on the catalyst surface. The presence of fluoride stabilizes the basic sites even at low temperature. The optimum amount of MgF 2
(Lewis acid sites) and Mg(OH) 2 (medium-strength basic sites) determines the performance of the nanocomposite catalysts, and MgF 1.5 (OH) 0.5 exhibits the best performance for producing C 13 (F 2 Ac) fuel precursors. The effect of different crystal
structures of cerous phosphate as solid acid catalysts on their catalytic performance
M. Baithy et al.